1. Field of the Invention
The present invention relates to a light irradiation device for irradiating a visible light and an ultraviolet ray, and more particularly to a light irradiation device suitable for a head lamp of an automobile.
2. Related Background Art
When an ultraviolet light is irradiated to a fluorescent material, the material tends to emit a visible light. Recently, a traffic system which uses such ultraviolet ray (particularly a near-ultraviolet ray (UV-A) of 330-400 nm) to detect a fluorescent material at a distant point has been discussed. FIG. 1 shows an example thereof in which a UV lamp 3 is added to a head lamp 2 of an automobile 1 and a UV (ultraviolet) ray emitted from the UV lamp 3 is irradiated to a pedestrian 4 at a distant point. In this case, if the pedestrian wears a cloth which contains many fluorescent materials such as cotton or nylon, a visible light (fluorescent) is emitted from the cloths when it is irradiated by the UV ray and the ray is caught by eyes of a driver to recognize the pedestrian 4.
The visible light of the head lamp 3 irradiates a relatively near point as shown by a broken line arrow in FIG. 1 in order to prevent the light from affecting to a facing car, and a limit of the irradiation distance is 40-50 meters. On the other hand, since the near ultraviolet ray does not affect to the facing car and is harmless to a human body, it may be emitted parallelly to the ground so that a pedestrian of 150 meters ahead can be recognize.
By the combination of the visible light and the ultraviolet ray, it is possible to construct a safer traffic system. In a prior art light irradiation device of this type, however, it is usual to separately arrange a light source for generating the visible light and a light source for generating the ultraviolet ray. However, the use of the two light sources is waste of energy and the construction of the device is complicated.